The JK Audio Auto Hybrid is a completely passive device with transformer coupled balanced inputs and outputs. Open one up and you'll find gold flashed connectors and switches, high quality components, all beautifully laid out. Overall this is a very robustly built interface.
They're an excellent way to get clean, solid Caller audio into your Program mix, and sending Program audio to your caller. With Balanced XLR I/Os, these boxes quickly interface with any console.
JK Audio's description tells it best:
Not just another half duplex auto-coupler.
This simple, passive, auto-answer/disconnect telephone line hybrid allows simultaneous send and receive audio through analog telephone lines. Suitable for monitoring remote locations, IFB feeds, and many simple studio, conferencing, and PA telephone interface applications.
Yes, you can send and receive audio at the same time. The dual transformer hybrid is capable of 20 dB nominal trans-hybrid loss. In other words, your transmit signal will appear mixed with the receive signal, but at a level 20 dB lower than it was sent into the phone line.
The “Auto” feature is very simple. When the “Auto” switch is selected, AutoHybrid will answer on the first ring. The phone line will remain off-hook, until either the Drop button is depressed, or until the phone company releases the line.
Female XLR: 1k ohms /500 mV RMS; -4 dBu nom.; +6 dBm max
Insertion Loss: 11dB Send XLR to Phone Line
Male XLR: 600 ohms / 200 mV RMS; -12 dBu nom.
Off-hook control (+5VDC Momentary)
Release Control (+5VDC Momentary)
OH LED Signal (pulled to ground on OH)
Phone Line: RJ11C
Aux Phone: RJ11C
Ringer: 0.8B REN
Isolation: 1500 VAC
Frequency Response: Telephone Side 200 Hz-3600 Hz
Size: 4” x 5” x 1.5” (10.5 x 13 x 4 cm)
Weight: 12 oz